The present invention relates generally to fiber-optic (fiber) based telecommunications networks having loop topology, and more specifically to the implementation of an Ethernet on such a network.
A standard implementation of a telecommunications network has a central office (CO) and three, or more, remote terminals (RTs) connected to the CO in a redundant ring structure. The CO contains the switching equipment and the loop is the intermediate network between the CO and the end-user. Typical networks are implemented in a redundant, counter-rotating configuration. Such networks may typically employ the synchronous optical network (SONET) standard. SONET defines a hierarchy of interface rates for different fiber-optic transmission systems to allow data streams at different rates to be multiplexed. Employing the SONET standard makes it possible for communication carriers to interconnect existing digital carrier and fiber systems. The RTs of the network have optical add/drop multiplexers (MUXs) through which data transmission access is provided. Each RT throughout the system may add or drop capacity from the network.
A typical ring is designed to carry 1,336 active telephone calls at 64 kbps using a data transmission speed of, for example, optical carrier-3 (OC-3), approximately 155 megabits per second. This equates to supporting approximately 5,000 residential telephone subscribers using a 4:1 concentration ratio. A typical RT may support 1,000-2,000 subscribers. This doesn""t allow bandwidth for other data transmission services (e.g., ADSL) that require 100 times as much speed.
Another drawback of a SONET network is that it is time division modulation (TDM) based. Therefore, once a particular amount of available bandwidth is allocated to a particular function, that bandwidth is not available for other purposes. This makes a SONET network poorly suited for data traffic. For example, a particular subscriber may have a T1 line that will be allocated 1.5 megabits per second on the network whether it""s being used or not.
A method is disclosed for overlaying a packet-based telecommunications network on a time division multiplex-based telecommunications network having a ring topology. Add-drop multiplexers are implemented at each node of the time division multiplex (TDM) based telecommunications system, the add-drop multiplexer comprising at least one wave division multiplexers. The TDM-based data is transmitted over a first light frequency and packet-based data is transmitted over a second light frequency.
Other features and advantages of the present invention will be apparent from the accompanying drawings, and from the detailed description, which follows below.